Electronic – Can you have “directional” wireless power transmission (to power an LED)

inductioninductivewireless

I've tried to research this, but the only circuit examples I can find use an "oscillating field".

I have a project where I would like to put two differently colored LEDs in an object, and depending on where on the "base" (or controlled by an MCU) one or the other color will light up.

My idea was to use "wireless power transmission" (because I don't want to put a battery in the object) and then control the direction of the field to dictate which LED lights up (similar to a "biderectional LED").
But I can only find circuits that use AC (to be more efficient‽), either with a capacitor & transistor or just a transistor and "self oscillation".

The Rx-coil probably can't have a bigger diameter than 2 (3cm MAX), the Tx-coil could be at least Ø5cm (potentially a bit bigger).

ETA: The distance between the coils could be minimum/best case ~5mm (with PLA plastic between them)

ETA2: This for an "interactive display piece": One location in the object lights up yellow, everywhere else it lights up blue.
It will be on for 8+ hours every day (which makes me hesitant to use batteries in the object).

Any suggestions?
Or will it just not be possible to do it on such low power?

Best Answer

My idea was to use "wireless power transmission" (because I don't want to put a battery in the object) and then control the direction of the field to dictate which LED lights up (similar to a "biderectional LED"). But I can only find circuits that use AC (to be more efficient‽), either with a capacitor & transistor or just a transistor and "self oscillation".

Polarity will not work; this sort of "wireless power transmission" is really a transformer, and transformers only pass AC.

You could potentially use the orientation of the field, ie, have two solutions at right angles to each other, but a lot of contemporary solutions have the field oriented vertically, so that won't work either.

Instead, what you'd probably want to do is to modulate information in a detail of the drive signal - possibly something as simple as a small change in frequency, or a pattern of pulses and gaps.

Or you could just use some cheap radio technology.

The advantage of the latter is that you could give in and use a battery for power after all, which you're likely to find quite a bit easier to get working.

Easiest still would be a battery and some reed switches, and then put magnets or electromagnets in the base; then you don't even need to do low-power design to preserve your battery, since the reed switch functions as an actual switch.